What Will a Large Earthquake be Like Flexible or Strong Lateral stiffness relies on flexing beams
Komando, Kim, Host has reference to this Academic Journal, PHwiki organized this Journal What Will a Large Earthquake be Like Tom Heaton Caltech Magnitude Paradox Seismologist Radiated energy increases by 32 times as long as each unit of magnitude. The number of earthquakes decreases by 10 times as long as each unit of magnitude. In Cali as long as nia, most of the energy is in earthquakes with magnitudes larger than 7.4. Large earthquakes do most of the work of plate tectonics. Although they are infrequent, they are inevitable. After the M 6.7 1994 Northridge earthquake seismologists said, this was only a moderate earthquake wait till you see a great one. Magnitude Paradox Engineer Perhaps there can be larger motions, but these are extreme examples of extraordinary events that shouldnt be used as long as building design. Eyewitness reports of the 1906 earthquake indicate that the shaking was comparable to that in 1994, but it lasted longer in addition to occurred over a larger area. Computer models shows that most of the risk comes from more frequent moderate size events. This building is designed as long as a M 8, the largest possible earthquake!
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Current model says most of the threat to downtown LA is not from the San Andreas fault
1906 M 7.8 San Francisco earthquake rupture with large ground displacement. Notice that the farm buildings were largely intact. Pt Reyes Station 1906 Current Building Code Current building codes are mostly prescriptive rules based on the building type in addition to seismic zone. Codes have been developed by fixing deficiencies from past earthquakes. If youve got a good building code, who needs a seismologist
How do buildings resist earthquake as long as ces Front View Top View Image: Courtesy EERI Tall Building Anatomy stiff Wooden Houses 7-11 stores Caltech High-rise buildings flexible
Flexible or Strong Stiff buildings tend to have high stresses, in addition to must there as long as e be strong. Making a building strong increases the stiffness, which increases the stresses, which increases the required strength of the building (a vicious circle). Making a building flexible tends to decrease the stress, but it also decreases the strength of a building (another vicious circle). Tall buildings are always designed to be flexible. Lateral stiffness relies on flexing beams Large de as long as mation should result in bent steel beams From the lab of Chia-Ming Uang, UC San Diego
Tall buildings cannot withst in addition to large Tilts Integrity of the columns is critical. Gravity loads are normally axial compressional loads on the columns. Tilted columns result in bending as long as ces on the columns caused by the weight of the building. Drift (i.e. column tilt) should not exceed 0.03 as long as tall MRF buildings. John Halls design of a 20-story steel MRF building that meets Cali as long as nia 1994 code (zone IV, site class C)
20-story steel-frame building subjected to a 2-meter near-source displacement pulse (from Hall) triangles on the frame indicate the failures of welded column-beam connections (loss of stiffness). Simulated de as long as mation of 20-story steel frame as long as the M6.9 1989 Loma Prieta Earthquake JBC is Japanese building code UBC is 1994 Cali as long as nia code
1906 ground motion simulation from Brad Aagaard (USGS) Simulated 20-story steel frame as long as a M 7.8 1906-like earthquake Yellow in addition to red are damaged beyond repair Pink is simulated collapse Large displacements can overwhelm base isolation systems 2-meter displacement pulse as input as long as a simulation of the de as long as mation of a 3-story base-isolated building (Hall, Heaton, Wald, in addition to Halling The Sylmar record from the 1994 Northridge earthquake also causes the building to collide with the stops
Isolator displacements (m) Most isolated buildings cannot exceed 0.4 m
Frame buildings can have also be built with concrete columns in addition to beams (as opposed to steel) 1971 San Fern in addition to o earthquake showed that many concrete frames were brittle Potential as long as collapse at drifts of about 0.01 (lower than as long as steel buildings) There are thous in addition to s of these buildings in Cali as long as nia in addition to occupants have not been notified Olive View Hospital M 6.7 1971 San Fern in addition to o Earthquake Northridge 118 FWY Example of failure of a brittle concrete column (pre-1975 code)
Conclusions Current probabilistic hazard analysis may seriously underestimate the importance of large earthquakes. Flexible buildings that rely on high ductility will be damaged beyond repair in large earthquakes in addition to many may collapse. Fix the pre-1994 steel welds! Notify occupants of pre 1975 brittle concrete frame buildings! Base isolation systems may be overdriven by large near-source ground motions. Strong shear-wall construction is best suited to resist large-magnitude earthquakes (your wooden house will per as long as m well). If it doesnt burn.
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